(a) Field of Invention
The present invention relates generally to luminaires which provide ambient uplighting and task-oriented downlighting. More specifically the invention relates to a luminaire mounted on a vertical surface, such as that used with partition panels or stanchions in modular office furniture systems, where the luminaire is a task/ambient luminaire having a compact profile and utilizing a twin tube lamp.
(b) Description of Related Art
Task-ambient luminaires are well known in the industry and are especially effective at achieving high quality illumination in open office environments. Generally, they are fashioned to mount to vertical surfaces such as open office workstation partitions, walls, stanchions, etc., and are designed to direct a portion of their output in a downward direction to illuminate work surfaces and to direct a portion of their output in an upward direction to illuminate ceilings and to give general diffuse lighting to the space. Downlight distributions that broadly illuminate a vertical privacy panel directly in front of the task area are also desirable where such panels occur. Commonly, such panels are 48″ to 60″ tall and incorporate a luminaire positioned along a top edge of the panel.
Linear type fluorescent lamps of nominal 1″ diameter (T8 lamps) or ⅝″ diameter (T5 lamps) are the most popular lamps for these type of task/ambient workstation applications. Consequently, installations typically consist of luminaires of about 6, 7, or 8 feet in length, each incorporating 3′, 4′, or 5′ long fluorescent lamps, singularly or in tandem, as dictated by the length of the unit. Generally, each workstation is provided with one such unit mounted along the top edge of the privacy panel that coincides with the primary task area of the workstation. (See, e.g., FIG. 1.) Especially large workstations and those with more than one primary task location may incorporate an additional unit. Although ambient lighting levels and unit power densities will vary somewhat based on workstation densities, each workstation receives relatively consistent task illuminance without the need for conventional supplementary task lights that otherwise do not contribute general ambient lighting to the office.
Recognizing that some open office configurations cannot accommodate relatively long, linear task/ambient luminaires, and recognizing that such luminaires may present barriers to worker interaction in open office environments where privacy partitions are intentionally very low or non-existent, it is advantageous to offer a compact task/ambient luminaire that has similar output. In as much as the cost of such a compact unit would be less than that of its traditional elongated version, such compact luminaires would be advantageously more affordable as well.
Compact long twin tube fluorescent lamps offering output nearly equal to that of comparable wattage linear lamps of twice their length are widely known and available. For example, a 22.5″ long 80-watt long twin tube compact fluorescent lamp that produces 6000 lumens is available in comparison to a 58.4″ long 80-watt high output T5 lamp that generates 7000 lumens. Similarly, a 21.1″ long 55-watt long twin tube compact fluorescent lamp that produces 4800 lumens is available in comparison to a 46.6″ long 54-watt high output T5 lamp that produces 5000 lumens. Although lamps with these relatively large wattages and outputs are not commonly employed in task and task/ambient luminaires, it is not uncommon for a typical workstation to employ 7 or 8 foot long luminaires employing two tandem mounted T8 or standard (lower) output T5 lamps totaling 50-65 watts and producing 5000-6000 lumens.
Compact fluorescent lamps may present the opportunity to offer comparable luminaires of reduced length, however their relatively larger cross-section and the relatively high luminous intensities associated with generating comparable output from a smaller source present unique challenges to the design of task/ambient workstation luminaires. For example, while a larger lamp cross-section suggests a larger luminaire profile to maintain efficiency and control, it is ultimately desirable to offer a luminaire that takes best advantage of the compact length and high luminous output of these lamps without compromising (increasing) luminaire profile. Similarly, it is desirable that the increased luminous intensity of these lamps not result in excessive workstation brightness and that an advantageous luminous balance be maintained in the workstation. Accommodation of the aforementioned single-ended compact lamps further requires that a lamp aligner/support be included in the luminaire design to support the lamp at a point distant from the lampholder/lamp base and maintain its alignment relative to the luminaire reflector and shielding components.
Particularly, a luminaire is desired which is compact in length and in profile but which provides a desirable luminous intensity and an even and balanced distribution thereof over a task area, for example, in a modular office workstation, and which provides a discrete lamp aligner/support for supporting the lamp and maintaining the lamp in a desired alignment relative reflecting and shielding components of the luminaire, and which is economical to manufacture, easy to assemble, and simple to install.